CONTROLS ON THE PRESERVATION OF ICHNOFOSSILS

Taphonomy, the study of fossilization, is an integral element of paleontology that can be put to constructive use in sedimentologic and paleoenvironmental studies. Like body fossils, trace fossils are subject to a wide range of taphonomic processes that influence (1) ichnologic integrity, the extent to which ichnofabrics reflect the complete range of activities of a community or communities of trace-making organisms, and/or (2) trace fossil visibility, the extent to which preserved ichnofossils are manifest or accessible to the viewer. The taphonomic state of a trace fossil assemblage or ichnofabric is controlled by a variety of interacting factors that generally fall within one of three categories: (1) physical environmental factors- e.g., substrate type, and rates and frequencies of deposition; (2) ecologic factors- e.g., infaunal tiering and behavioral routines of tracemakers; and (3) diagenetic factors- preferential mineralization, general lithification, and, in the case of surface exposures, weathering. Varying combinations of these factors result in preservation states ranging from poor to excellent. Regardless of preservation state, careful consideration of ichnofossil taphonomy can help assess aspects of depositional regime, tracemaker paleobiology, and postdepositional histories of substrates. Trace fossil assemblages characterized by relatively high ichnologic fidelity, trace fossil visibility, or both may be particularly informative and, hence, can be considered as ichnofossil-lagerstätten.